Conventionally, a hydraulic non-stage transmission and axle driving apparatus housed in a casing is well known, as disclosed in, for example, U.S. Pat. Nos. 4,932,209 and No. 4,986,073.
Such axle driving apparatus has been used mainly in small-sized vehicles, such as a mower tractor loading thereon a vertical type engine. In such a construction, the casing of the axle driving apparatus is formed by joining two main casing halves with each other, the junction surface therebetween is incidental with a plane including the longitudinal axis of the axles.
As a result, the above-mentioned vehicle has the following disadvantages:
First, an input pulley for inputting engine power to the axle driving apparatus is mounted high with respect to the axis of the driving axle so as to restrict the height of a platform for the vehicle. Hence, the platform cannot be low, which hinders the ability to miniaturize the vehicle. On the other hand, when a single belt transmission mechanism is used to couple the engine with the axle driving apparatus, the engine is positioned high to correspond to the position of the input pulley, whereby the vehicle has a high center of gravity, which affects the running stability of the vehicle.
Second, for maintenance of the transmission mechanism, such as a hydraulic non-stage transmission housed in the casing, if the casing is dismantled, the axles are also dismantled together therewith, whereby the axle driving apparatus itself should be removed from a frame, thereby causing much trouble.
Third, a bearing for supporting the axle to the casing is held in part to the respective casing halves. However, in the case where the respective casing halves are molded by an aluminum die-cast or the like, it is difficult to exactly obtain dimensional precision of the part holding the bearing. As the result, the axle can easily cause a backlash, the life span of the bearing is reduced, and oil may leak from a sealing portion of the axle.
Fourth, each casing half bears a load applied to the axle, so that the number of mounting bolts for the casing is increased to increase its rigidity, thereby requiring much time to assemble the axle driving apparatus.